PURPOSE: To prevent danger in turning on very wet ground, by interlocking the operating device of a stepless transmission with a very wet ground turning equipment for a combine or the like which turns on the very wet ground such as a paddy field, so that the transmission performs speed reduction when the turning equipment is put in operation.

CONSTITUTION: When a left steering lever 36 is moved along a longitudinal groove 35a and then along a transverse groove 35b for left turning on very wet ground, a left side clutch 27 is disengaged from a center gear 25. At the same time, a shifter 49a is operate through a wire 43 etc. to engage a very wet ground turning clutch 33 with a gear 32. The torque of a gear 30' is transmitted to a left shaft gear 30 through a gear 31, the clutch 33, the idle gear 32 and a large-width gear 34 to rotate the gear 30 in the opposite direction to the gear 30' to reverse a left sprocket shaft 9 as to a right sprocket shaft 9' to turn a combine 1 on the very wet ground. When a limit switch 51 is turned on by putting the left steering lever 36 in the transverse groove 35b, a speed reducing solenoid is energized to retract a cylinder to put a speed change pulley in a low speed position to drive the combine 1 at a low speed.